PS3 YLOD Algorithm Investigation help?

I was wondering if the algorithm that the PS3, uses to show YLOD, is already known ??? Has it been completely investigated ?? How does the PS3 determine, OK, lets show YLOD to the frustrated gamer ??? Which component, runs the algorithm, and what all inputs does it require for judgement ?

Then, is there some flowchart that might tell, say, check a, b & c points, with a scope, if they are asserted, then it means GPU got disconnected/dead, and we need a reflow/reball, else don't waste time doing a reflow, check for eg. the power conditioning circuts ?

Most of the information on interwebs say YLOD=Loose GPU Contacts, Is it really only so ? Is there an authoritative document ?